Scores of flights have been cancelled and drivers were warned to take care as a fresh freezing blast of weather dubbed the "mini beast from the east" swept in.
There was snowfall overnight over much of eastern England and Scotland as the cold snap sets in with icy and "bitterly cold" winds that will leave some areas feeling as cold as -8C.
An amber weather warning for snow and ice is in place across north-west England, Yorkshire and the Midlands, as well as in London, the South East, and east of England, from 4pm on Saturday until 9am on Sunday.
And a yellow warning for snow and ice in force for the entire day covers nearly the whole of Britain.
More than 70 flights to or from Heathrow Airport on Saturday were cancelled due to the weather.
Most of the cancellations were on short-haul routes, although British Airways services to New York and Chicago were among those affected.
Drivers have also been urged to be prepared before setting out on journeys this weekend, with Highways England advising motorists to avoid trans-Pennine roads "if possible".
Among the roads which drivers are being urged to avoid are the M62 (junctions 21 to 25), A628 and A66.
There were also calls not to drive on the M1 between junctions 35 (Rotherham) and 47 (Garforth), the M606 near Bradford and the M621 near Leeds unless absolutey necessary.
Highways England's head of road safety, Richard Leonard, said: "Our gritter drivers will be out treating our roads around the clock but it is still important to drive to the conditions when snow is forecast.
"Make sure you keep your distance and reduce your speed if you need to travel because, even in conditions that seem normal and when the snow is not settling, it can be slippery if ice patches have formed or where fresh salt has not been worked into the carriageway.
"Drivers should plan their journeys, monitor weather reports and pack a snow kit of blankets, food, water and a shovel if they really need to travel."
Network Rail, which is responsible for Britain's rail tracks, is running empty trains to help keep the network clear of snow.
It is also carrying out checks on heating systems designed to avoid sections of track from freezing.
Forecasters said much of eastern England and Scotland had seen a smattering of the snow during the night, with snowfall moving westwards towards the Midlands and Wales.
Most places are likely to see some wintry showers by the end of the day, with gusty winds bringing "bitterly cold" temperatures.
Met Office meteorologist Alex Burkhill said: "There are some very strong winds, meaning it could feel as low as minus 7 or minus 8 for some people."
Sunday is also likely to see further snow, especially for parts of the South West, whereas much as 25cm could fall on higher ground.
The cold weather should only last a few days though - by Tuesday, temperatures will begetting back to average for the time of year.